Sheet feeding apparatus and image forming apparatus

ABSTRACT

A sheet feeding apparatus having sheet stacking means movable up and down with a plurality of sheets stacked thereon, sheet feeding means for feeding out the sheets stacked on the sheet stacking means and control means for moving the sheet stacking means up and down so that during the supply of the sheets to the sheet stacking means and during the taking-out of the sheets from the sheet stacking means, the upper surface of the sheets stacked on the sheet stacking means may be automatically moved to a sheet supplying position and a sheet taking-out position set between the upper limit position and the lower limit position in the range of the upward and downward movement of the sheet stacking means each time the sheet is supplied and each time the sheet is taken out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a sheet feeding apparatus provided in an image forming apparatus such as a copying machine, a facsimile apparatus or a printer for feeding sheets one by one, and particularly to a sheet feeding apparatus capable of containing therein and feeding a great amount of sheets in a copying machine or the like.

2. Description of the Related Art

A sheet feeding apparatus disposed in a conventional image forming apparatus such as a copying machine is described in Japanese Patent Application Laid-Open No. H03-182428. This will hereinafter be described with reference to FIGS. 9 to 12A and 12B of the accompanying drawings.

As shown in FIG. 9, a paper deck 100 connected to a side of a copying machine 400 is provided with a housing 101 and a container 102 drawable out and containable relative to the housing 101. The container 102 is provided with a lifter plate 103 movable up and down by a lifter motor 111 shown in FIGS. 10A to 10D, and a great amount of sheet stack S can be stacked on the lifter plate 103. The supply sheets S is effected with the container 102 drawn out of the housing 101.

Also, a sheet upper surface detection sensor 106 is provided above the container 102, and the lifter plate 103 has its upward movement controlled on the basis of the detection by the sheet upper surface detection sensor 106 so that a predetermined height may be maintained during a sheet feeding operation.

A sheet feeding mechanism 200 is provided with a pickup roller 201, a pair of separating rollers 202 and a pair of drawing-out rollers 204 in succession from the upstream side, and conveys the sheets S to the downstream side. The pair of separating rollers 202 is comprised of a forwardly rotated feed roller and a retard roller which is provided with a predetermined torque limiter coaxially therewith, and to which reverse rotative drive is transmitted, and this pair of separating rollers 202 prevent the double feeding of two or more sheets. When the sheets are fed and the position of the upper surface of the stacked sheets is lowered, control is effected such that the lifter plate 103 is moved up by the signal of the sheet upper surface detection sensor 106 and the position of the upper surface of the sheets becomes a substantially constant position.

Description will now be made of the sheet supplying operation to the paper deck 100. FIGS. 10A to 10D are illustrations of the supplying operation when the sheets are absent. FIG. 11 is a flow chart of the control during the sheet supplying operation.

In FIGS. 10A to 10D, h1 is the position (sheet supplying position) of the upper surface of the sheet stack S (the upper surface of the lifter plate 103 when the sheets are not stacked) stacked on the lifter plate 103 when the sheets are supplied, and is a position at which the upper surface of the sheets (the upper surface of the lifter plate 103) is detected by a position sensor 107. Also, h2 is the position of the upper surface of the sheets when the sheets are fed out by the pickup roller 201. Also, h3 is the lower limit position when the lifter plate 103 has been moved down to the lowermost level, and is a position detected by a lower limit detection switch 110.

When as shown in FIG. 10A, the sheets on the lifter plate 103 become exhausted, the absence of the sheets is detected by a sheet presence or absence detection sensor, not shown, and the lifter plate 103 is moved down by the lifter motor 111, and the lifter motor 111 is stopped when the position sensor 107 lying at a location downwardly separate by a distance 12 has become on to off. This stopped position is the sheet supplying position h1.

Next, as shown in FIG. 10B, a worker draws out the container 102 and performs sheet supplying work. The distance 12 between the sheet supplying height h1 and the sheet supplying position h2 is set to a value greater than the thickness 11 of one pack of the sheet stack S and therefore, the supply of the sheet stack S can be effected appropriately.

The position sensor 107 is rendered on by the supplied sheet stack S, and again the lifter motor 111 moves the lifter plate 103 down. Then, when as shown in FIG. 10C, the position sensor 107 becomes off at a position where at the sheet stack S has become lower than the position sensor 107, the lifter motor 111 is stopped. Accordingly, again when the worker continuedly effects sheet supply, the upper surface of the supplied sheets lowers to the sheet supplying position h1 and therefore, supply is always possible in a state of good working property.

Describing this with reference to the flow chart of FIG. 11, at a step (hereinafter abbreviated as S) 1, the sheet stack S is supplied to the lifter plate 103 located at the sheet supplying position h1, whereupon the position sensor 107 becomes on, and at S2, the lifter motor 111 again moves the lifter plate 103 down. Then, at S3, whether the lower limit detection switch 110 has detected the lifter plate 103 is judged, and if it has not detected the lifter plate, return is made to S1. When at S, the sheet stack S becomes lower than the position sensor 107 and the position sensor 107 becomes off, advance is made to S4, where the lifter motor 111 is stopped.

Such supply of the sheet stack S is repeated (S1-S3) and when at S3, the lifter plate 103 goes down to the lifter lower limit position h3 and the lower limit detection switch 110 becomes on, at S4, the lifter motor 111 is stopped and the going down of the lifter plate 103 is stopped. The stacked amount of the sheet stack S at this time becomes a maximum stacked amount.

In the above-described conventional sheet feeding apparatus, however, operability is good when during the sheet supplying operation, the lifter plate 103 goes down and supplies the sheets, but there has been the problem that an inconvenience is encountered when the sheets are interchanged in order to change, for example, the kind or size of the sheets.

That is, in a case as shown in FIG. 12A wherein the sheets contained in the paper deck 100 are relatively many, when the container 102 is drawn out and the kind of the sheets is to be interchanged, the lifter plate 103 goes down until the side of the remaining sheet stack S renders the position sensor 107 off. Then as shown in FIG. 12B, the worker takes out the remaining sheets and supplies sheets desired to be interchanged with. At this time, the lifter plate 103 is at a deep position in the container 102 and therefore, to take out all of the sheets stacked on the lifter plate 103, the worker need insert his hand into the deep position and take out the sheets.

Also, when after the sheets have been taken out, another sheet is to be supplied, the worker inserts his hand into a deep position and drops the sheet from above, and this has led to the problem that the working property is very bad. Also, there has been the problem that the worker is compelled to perform such an operation of a bad working property, whereby there arises a situation in which the remarkable lowering of the reliability of the apparatus such as paper jam or faulty recording attributable to the breakage of the sheets during the setting thereof is caused.

Particularly in recent years, with the spread of print on demand (POD), there has been heightened the desire of the market for providing a great deal of prints with high productivity, and printing on a variety of sheet materials has been desired and therefore, the work of frequently interchanging the sheets in such a paper deck of large capacity is steadily in the tendency toward an increase, and an improvement in the working property of interchanging the sheets is demanded.

SUMMARY OF THE INVENTION

So, the present invention has as its object to provide a sheet feeding apparatus which can well accomplish the supply of sheets and sheet interchanging work.

The present invention provides a sheet feeding apparatus having:

-   -   sheet stacking means movable up and down with a plurality of         sheets stacked thereon;     -   sheet feeding means for feeding out the sheets stacked on the         sheet stacking means; and     -   control means for automatically moving an upper surface of sheet         stacked on said sheet stacking means to a sheet supplying         position each time the sheet is supplied and to a sheet         taking-out position each time the sheet is taken out, wherein         said sheet supplying position and said sheet taking-out position         are respectively set between an upper limit position and a lower         limit position in a range of the upward and downward movement of         said sheet stacking means.

Also, the present invention provides a sheet feeding apparatus having:

-   -   a lifter plate provided for upward and downward movement;     -   a lifter motor for moving the lifter plate up and down;     -   a pickup roller for feeding out sheets stacked on the lifter         plate; and     -   a controller for controlling the lifter motor to thereby move         the lifter plate up and down;     -   wherein the controller moves automatically moves an upper         surface of sheet stacked on said lifter plate to a sheet         supplying position each time the sheet is supplied and to a         sheet taking-out position each time the sheet is taken out,         wherein said sheet supplying position and said sheet taking-out         position are respectively set between an upper limit position         and a lower limit position in a range of the upward and downward         movement of said lifter plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an image forming apparatus provided with a sheet feeding apparatus according to a first embodiment of the present invention.

FIGS. 2A, 2B, 2C and 2D are illustrations illustrating the operation of the sheet feeding apparatus in FIG. 1 during the supply of sheets.

FIGS. 3A, 3B and 3C are illustrations illustrating the operation of the sheet feeding apparatus in FIG. 1 during the interchange of the sheets.

FIG. 4 is a flow chart of the sheet supply and interchange control of the sheet feeding apparatus in FIG. 1.

FIG. 5 is a block diagram of a controlling position for effecting the control of the sheet feeding apparatus in FIG. 1.

FIGS. 6A, 6B and 6C are illustrations illustrating the operation of a sheet feeding apparatus according to a second embodiment of the present invention during the supply of sheets.

FIGS. 7A, 7B and 7C are illustrations illustrating the operation of the sheet feeding apparatus in FIGS. 6A to 6C during the interchange of the sheets.

FIG. 8 is a cross-sectional view of a sheet deck according to another embodiment.

FIG. 9 is a cross-sectional view of an image forming apparatus provided with a conventional sheet feeding apparatus.

FIGS. 10A, 10B, 10C and 10D are illustrations illustrating the supplying operation of the conventional sheet feeding apparatus during the supply of sheets.

FIG. 11 is a flow chart of the control during the sheet supplying operation of the conventional sheet feeding apparatus.

FIGS. 12A and 12B are illustrations of the supplying operation of the conventional sheet feeding apparatus during the interchange of the sheets.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of a sheet feeding apparatus according to the present invention will hereinafter be described with reference to FIGS. 1 to 5. As shown in FIG. 1, in the present embodiment, a paper deck 100 as an example of a sheet feeding apparatus disposed in parallel to a copying machine 400 as an example of an image forming apparatus for feeding sheets to an image forming portion 406 in the copying machine 400 will be described as an example.

(Construction of the Copying Machine)

Referring to FIG. 1, a paper cassette 402 and paper decks 404 containing the sheets therein are provided in the copying machine 400, and the sheets contained therein are supplied to the image forming portion 406 and images are formed thereon. The image forming portion 406 is of an electrophotographic type comprised of a photosensitive drum 408, etc., and a toner image developed on the peripheral surface of the photosensitive drum 408 is transferred to the supplied sheet, and is fixed by a fixing device 410 on the downstream side.

In the upper portion of the copying machine, there is disposed an original reading apparatus 412 comprising a scanner for reading an original, and an automatic original conveying apparatus for automatically conveying the original.

This copying machine has a network cable, not shown, connected thereto, and also has a printer function capable of forming data from an external personal computer or the like into an image.

(Sheet Feeding Apparatus)

In FIG. 1, the paper deck 100 is comprised of a housing 101 and a container 102 capable of being drawn out and contained relative to the housing 101. The container 102 is provided with a lifter plate 103 as sheet stacking means, and a great amount of sheet stack S can be stacked on the lifter plate 103. The supply of the sheet S is effected with the container 102 drawn out of the housing 101. The contained sheet stack S has its leading and trailing edges regulated by a leading edge regulating plate 104 and a trailing edge regulating plate 105, respectively, and has its opposite side edges regulated by side regulating plates, not shown.

By these regulating plates for regulating the four sides of the sheet stack S, the sheet stack S stacked on and contained in the paper deck 100 can be stably held at a predetermined position. Also, a sheet upper surface detection sensor 106 is provided above the container, and during a feeding operation, the lifter plate 103 has its upward movement controlled so that the upper surface of the sheets may be maintained at a constant height on the basis of the detection by the sheet upper surface detection sensor 106. The lifter plate 103 is movable up and down between the upper limit position and the lowermost lower limit position of a sheet feeding position H2 by a lifter motor 111.

A sheet feeding mechanism 200 as sheet feeding means is provided above the container 102, and the sheet feeding mechanism 200 is provided with a pickup roller 201, a pair of separating rollers 202 and a pair of drawing-out rollers 204 in succession from the upstream side, and feeds the sheet S to the copying machine 400. The pair of separating rollers 202 comprise a forwardly rotated feed roller and a retard roller provided with a predetermined torque limiter coaxially therewith and to which reverse rotative drive is transmitted, and the pair of separating rollers 202 prevents the double feeding of two or more sheets. When the sheets are fed and the position of the upper surface of the sheets are lowered, the lifter plate 103 is moved up by the signal of the sheet upper surface detection sensor 106, and control is effected so that the position of the upper surface of the sheet stack S may be a substantially constant position as the sheet feeding position H2.

As shown in FIGS. 2A to 2D and 3A to 3C, the container 102 is provided with two sheet surface detection sensors 108 and 109 which are position detecting means for controlling the upward and downward movement of the lifter plate 103. The sheet surface detection sensors 108 and 109 serve to detect the sheet stack stacked on the lifter plate 103 or the lifter plate 103, and on the basis of the timing at which the sheet surface detection sensors 108 and 109 become on to off or become off to on, the position of the upper surface of the sheets or the upper surface of the lifter plate 103 in a height direction can be detected.

FIG. 5 shows a control block diagram. The control of the lifter motor 111 for the upward and downward movement of the lifter plate 103 is effected by a controller C which is control means on the basis of the detection by the sheet surface detection sensors 108 and 109.

(Sheet Supplying Operation)

Description will now be made of a sheet supplying operation to the paper deck 100. FIGS. 2A to 2D are illustrations of the supplying operation when the sheets are absent, and FIG. 4 is a flow chart of the control by the controller C during the sheet supplying operation.

When as shown in FIG. 2A, the sheets in the paper deck 100 become exhausted, the absence of the sheets is detected by a sheet presence or absence detection sensor, not shown, and by the lifter motor 111 for driving the lifter plate 103 upwardly and downwardly, the lifter plate 103 is lowered from the sheet feeding position H2, and the sheet surface detection sensor 108 is rendered on to off by the lifter plate 103, and subsequently the sheet surface detection sensor 109 is rendered off to on by the lifter plate 103, whereupon the lifter motor 111 is stopped. This stopped position is a sheet supplying position H1A downwardly separate by a distance L2 from the sheet supplying position H2. Thus, the sheet supplying position H1A is determined by a height at which the sheet surface detection sensor 108 becomes on to off and the sheet surface detection sensor 109 becomes off to on.

Next, as shown in FIG. 2B, the worker draws out the container 102 and performs the supplying work. Here the distance L2 between the sheet supplying position H1A and the sheet feeding position H2 is set to a value higher than the thickness L1 of one pack of the sheet stack S and therefore, the supply of the sheet stack S can be effected in an appropriate state. When the sheet stack S is supplied, the sheet surface detection sensor 108 becomes off to on.

Subsequently, when as shown in FIG. 2C, the sheet stack S is supplied, the lifter motor 111 moves the lifter plate 103 down. When the sheet surface detection sensor 108 is rendered off from its on state by the supplied sheet stack, the lifter motor 111 is stopped. This stopped position is a position at which the upper surface of the stacked sheet stack S coincides with the sheet supplying position H1A.

Then, as shown in FIG. 3D, the supplying operation for the sheet stack S is continuedly performed and the lifter plate 103 is moved down and is detected by a lower limit detection switch 110, whereupon a maximum stack amount of sheets are contained.

The control of this sheet supplying operation will be described here with reference to the flow chart of FIG. 4.

When as shown at the step 1 of FIG. 4, the sheet surface detection sensor 108 is rendered on by the supplied sheet stack S, advance is made to a step 2, where the lifter motor 111 moves the lifter plate 103 down. If at a step 3, the deck lower limit detection switch 110 being at a lifter lower limit position H3 is in its off state, return is made to the step 1. Then, as long as at the step 1, the sheet surface detection sensor 108 is in its on state, the lifter plate 103 is moved down by the lifter motor 111 (step 1 to step 3).

When at the step 1, the lifter plate 103 is moved down and the sheet stack S becomes lower than the sheet surface detection sensor 108 and the sheet surface detection sensor 108 becomes off, advance is made to a step 5. If at the step 5, the sheet surface detection sensor 109 is in its on state, return is made to the step 4, where the lifter motor 111 is stopped.

When this lifter motor 111 has been stopped, the upper surface of the stacked sheet stack S is at the sheet supplying position H1A, and when in this state, the sheet stack S is further supplied, the sheet surface detection sensor 108 is again rendered on by the sheet stack S supplied at the step 1. The above-described steps 1 to 3 are then repeated, whereby the lifter plate 103 is moved down until the upper surface of the sheet stack S comes to the sheet supplying position H1A, and when at the step 1, the sheet surface detection sensor 108 becomes off, advance is made to a step 5 and a step 4, where the lifter motor 111 is stopped.

When in the course in which the above-described control is repeated, the lower limit detection switch 110 becomes on at the step 3, a maximum stack amount of sheets are thus contained, and advance is made to the step 4, where the lifter motor 111 is stopped. The maximum stack amount of the sheet stack S at this time realizes 3,500 sheets.

Accordingly, again when the worker continuedly performs the supply of the sheets, the upper surface of the supplied sheet stack S lowers to the sheet supplying position H1A and therefore, supply is always possible in a state of good operability.

(Taking-Out of the Sheets)

Next, FIGS. 3A to 3C are illustrations of the taking-out operation during sheet interchange, and the sheet taking-out operation will hereinafter be described with reference to these figures.

When as shown in FIG. 3A, the container 102 is drawn out during the presence of the sheets, the lifter plate 103 is moved down until the upper surface of the sheet stack S comes from the sheet feeding position H2 to the sheet supplying position H1A, that is, until the sheet surface detection sensor 108 becomes off.

When subsequently, as shown in FIG. 3B, the worker takes out the upper sheet stack of the sheet stack S for the interchange of the sheets, the sheet surface detection sensor 109 becomes off and therefore, the lifter motor 111 moves the lifter plate 103 up until the sheet surface detection sensor 109 becomes on, and moves the position of the upper surface of the sheets up. The position of the upper surface of the sheets when the lifter plate 103 has been stopped is defined as a sheet taking-out position H1B. When the upper sheet stack of the sheet stack S is further taken out, the sheet surface detection sensor 109 again becomes off, and the lifter plate 103 is moved up until the position of the upper surface of the sheets becomes the sheet taking-out position H1B.

Each time the sheet stack S remaining in the container 102 is thus taken out by several installments, the lifter plate 103 is moved up, and each time, the position of the uppermost surface of the stacked sheets moves to the sheet taking-out position H1B.

After as shown in FIG. 3C, the sheets S have been completely taken out, the lifter plate 103 itself renders the sheet surface detection sensor 109 on and the lifter plate 103 is stopped at that position. Here, the worker can perform the work of supplying the sheets to be interchanged, and when be supplies the sheet stack to be interchanged, the above-described supply control of the sheets is effected. Then, the supplying operation can be performed at an appropriate height of the lifter plate 103. The difference between the sheet supplying position H1A and the sheet taking-out position H1B in the height direction is minute if the sheet surface detection sensors 108 and 109 are provided in proximity to each other.

The control of this taking-out of the sheets will now be described with reference to the flow chart of FIG. 4.

When the sheet stack S is taken out from the state of FIG. 3A, at a step 1, the sheet surface detection sensor 108 becomes off and advance is made to a step 5. At the step 5, as shown in FIG. 3B, the sheet surface detection sensor 109 is also in its off state and therefore, advance is made to a step 6, where the lifter plate 103 is moved up by the lifter motor 111.

Then, at the step 5, the sheet surface detection sensor 109 detects the sheet stack S, whereupon advance is made to a step 4, where the lifter motor 111 is stopped. At this time, the position of the upper surface of the sheet stack S becomes the sheet taking-out position H1B. By this control being repeated, as shown in FIG. 3C, the lifter plate 103 is stopped at the sheet taking-out position H1B and waits for the supply of the sheets to be interchanged.

As described above, in the paper deck 100 of large capacity, the worker, during the supply of the sheet stack, can supply the sheet stack S with the upper surface of the sheet stack S moved to the sheet supplying position H1A each time the sheet stack S is stacked, and when the sheets are to be interchanged, the worker can take out the sheet stack with the upper surface of the sheet stack S moved to the sheet interchanging position H1B each time the sheet stack is taken out. That is, if the sheet stack is supplied, the above-described supply control of the sheets is automatically effected, and if the sheets are taken out, the above-described taking-out control of the sheets is automatically effected and therefore, the worker need not perform an operation or the like for changing over the control.

As described above, the supplying work property during the absence of the sheets is maintained and yet, it is made possible for the uppermost sheet surface or the upper surface of the lifter plate to keep a sheet supplying position always good in the sheet supplying work property. Also during the interchange of the sheets, it is made possible for the upper surface of the sheet to keep a sheet taking-out position good in the sheet interchanging work property. Thereby, the worker need not stretch his hand to a position deeper than necessary and work, and the work of taking out the remaining sheets and the work of interchanging the sheets can be markedly improved, and during the absence of the sheets and during the interchange of the sheets, always good supply and interchange of the sheets can be done.

By adjusting the timing at which the lifter motor 111 is stopped after the sheet surface detection sensor 108 has become off when the sheets are to be supplied, and the timing at which the lifter motor 111 is stopped after the sheet surface detection sensor 109 has become on when the sheets are to be taken out, it is also possible to set the sheet supplying position H1 and the sheet taking-out position H4 to the same position in the height direction.

A second embodiment of the present invention will now be described with reference to FIGS. 6A to 6C and 7A to 7C. Members overlapping those in the above-described first embodiment are given the same reference numerals and need not be described. Also, operations and control not described are the same as those in the first embodiment and therefore need not be described.

While in the first embodiment, the sheet surface detection sensors 108 and 109 are provided in proximity to each other in the vertical direction, in the second embodiment, they are disposed with a great distance therebetween. In the other points, the construction of the second embodiment is the same as that of the first embodiment.

(Sheet Supplying Operation)

When as shown in FIG. 6A, the sheets in the paper deck 100 have become exhausted, the absence of the sheets is detected by the sheet presence or absence detection sensor, not shown, and the lifter plate 103 is moved down from the sheet feeding position H2 by the lifter motor 111 for driving the lifter plate 103 up and down, and when the sheet surface detection sensor 108 is rendered on to off by the lifter plate 103 and the sheet surface detection sensor 109 is rendered off to on by the lifter plate 103, the lifter motor 111 is stopped.

When subsequently, as shown in FIG. 6B, the sheet stack S is supplied, the sheet surface detection sensor 108 becomes off to on, and the lifter motor 111 moves the lifter plate 103 down.

When as shown in FIG. 6C, the lifter plate 103 is moved down, the sheet surface detection sensor 108 becomes off from its state rendered on by the sheet stack, and after a predetermined time has elapsed, the lifter motor 111 is stopped. This stopped position is a position in which the sheet surface detection sensor 109 does not become off and the sheet stack has come near the sheet surface detection sensor 109. The upper surface of the sheet stack S stacked on the lifter plate 103 at this time is a sheet supplying position H1C.

Also, when the supplying operation of the sheet stack S is further performed from the state shown in FIG. 6C, the lifter plate 103 is moved down until the upper surface of the supplied sheet stack S assumes the sheet supplying position H1C. Then, the supply of the sheet stack S is repeated, whereby the lifter plate 103 is sequentially moved down and is detected by the lower limit detection switch 110, whereupon the lifter plate 103 is stopped and a maximum stack amount of sheets are contained.

When the sheet surface detection sensor 108 becomes off from a state in which it is rendered on by the supplied sheet stack, and then to stop the lift motor 111 when the upper surface of the sheet stack S has assumed the sheet supplying position H1C in which it has come near the sheet surface detection sensor 109, the number of revolutions of the lifter motor 111, or in the case of a pulse motor, the pulse number can be counted and on the basis thereof, the lifter motor 111 can be stopped.

Also, design may be made such that when the absence of the sheets is detected and the lifter plate 103 has been moved down from the sheet feeding position H2, after a predetermined time has elapsed after the sheet surface detection sensor 108 has detected the lifter plate 103, the lifter motor 111 is stopped to thereby stop the lifter plate 103 so that the upper surface of the lifter plate 103 may coincide with the sheet supplying position H1C.

(Taking-Out of the Sheets)

Next, FIGS. 7A to 7C are illustrations of the taking-out operation during the interchange of the sheets, and the taking-out operation will now be described with reference to these figures.

When as shown in FIG. 7A, the container 102 is drawn out during the presence of the sheets therein, the lifter plate 103 is moved down until the uppermost sheet surface of the sheet stack S shifts from the sheet feeding position H2 and the sheet surface detection sensor 108 becomes off.

When subsequently, as shown in FIG. 7B, the worker takes out the upper sheet stack of the sheet stack S for the interchange of the sheets, the sheet surface detection sensor 109 becomes on to off, and the lifter motor 111 move the lifter plate 103 up to thereby move the position of the upper surface of the sheets up. Then, the lifter plate 103 is stopped after a predetermined time has elapsed after as shown in FIG. 7C, the sheet surface detection sensor 109 has been rendered on by the upward movement of the lifter plate 103. This stopped position is a position in which the sheet surface detection sensor 108 does not become on and the sheet stack has come near the sheet surface detection sensor 108. The upper surface of the sheet stack S stacked at this time is a sheet supplying position H1D.

When the upper sheet stack of the sheet stack S is further taken out, the sheet surface detection sensor 109 again becomes off, and the lifter plate 103 is moved up until the position of the upper surface of the sheets becomes a sheet taking-out position H4D.

Each time the sheet stack S remaining in the container 102 is thus taken out in several installments, the lifter plate 103 is moved up and each time, the position of the upper surface of the stacked sheets moves to the taking-out position H4D. After the sheet stack S has been completely taken out, the lifter plate 103 itself renders the sheet surface detection sensor 109 on to off to thereby stop the lifter plate 103. Here, the worker can do the work of supplying the sheets to be interchanged, and when be supplies the sheet stack to be interchanged, the above-described supply control of the sheets is effected.

To stop the lifter motor 111 when the sheet stack is taken out, whereby the lifter plate 103 is moved up and the sheet stack S renders the sheet surface detection sensor 109 on and the lifter plate 103 is further moved up and has come to a sheet taking-out position H1D in which the sheet stack has come near the sheet surface detection sensor 108, the number of revolutions of the lift motor 111 or in the case of a pulse motor, the pulse number thereof can be counted and the lift motor 111 can be stopped on the basis thereof.

In the present embodiment, the sheet supplying position H1C which is the position of the upper surface of the lifter plate 103 when the sheets are supplied or the upper surface of the stacked sheet stack S can be set to a position higher than the sheet taking-out position H1D which is the position of the upper surface of the sheet stack S when the sheets are taken out. By the sheet supplying position H1C being made low and the sheet taking-out position H1D being made high and these two positions being set to different positions, as described above, a space in the height direction when the sheets are supplied can be secured and even the unevenness of the supply amount in one installment can be coped with and the operability is improved, and when the sheets are to be taken out, the sheet stack can be set at a higher position and therefore, the operability is more improved.

Another embodiment of the sheet feeding apparatus according to the present invention will now be described with reference to the drawing. FIG. 8 is a cross-sectional view of the sheet feeding apparatus according to the present embodiment. Members overlapping those in the above-described first embodiment are given the same reference numerals and need not be described. Also, operations and control not described are the same as those in the first embodiment and therefore need not be described.

As shown in FIG. 8, in the sheet feeding apparatus according to the present embodiment, as the position detecting means for effecting the control of the upward and downward movement of the lifter plate 103, a sheet surface detection sensor 113 is provided instead of the sheet surface detection sensors 108 and 109 according to the first embodiment. The sheet surface detection sensor 113 is an optical sensor such as a CCD, and extends so as to detect the whole of the container 102 in the vertical direction (the uppermost sheet surface and the entire movement range of the lifter plate 103), and detects the uppermost sheet surface in the container 102 and the upper surface position level of the lifter plate 103.

When the upper surface of the sheet stack S or the sheets are not stacked, the upper surface of the lifter plate 103 is detected by the sheet surface detection sensor 113 and the lifter plate 103 is moved up and down so as to assume a predetermined position. That is, when the upper surface of the sheets has assumed a position higher than the predetermined position when the sheets have been supplied, the lifter plate 103 is moved down by the lifter motor 111, and when the upper surface of the sheets has assumed a position lower than the predetermined position when the sheets have been taken out, the lifter plate 103 is moved up by the lifter motor 111. When as described above, the position of the upper surface of the sheets has fluctuated, the lifter plate 103 is moved up or down so as to be returned to the predetermined position.

During the supply of the sheets and during the taking-out of the sheets, the upper surface of the sheets can be moved to the predetermined position to thereby make the sheet supplying position and the sheet taking-out position the same, but the position of the uppermost sheet surface or the upper surface of the lifter plate 103 can be linearly detected by the sheet surface detection sensor 113 and therefore, the position (predetermined position) of the upper surface of the sheets during the supply and interchange of the sheets can also be changed. That is, when the sheets have been supplied, the lifter plate 103 is further moved down from the predetermined position to thereby bring about a sheet supplying position, and when the sheets are to be taken out, the lifter plate 103 is further moved up beyond the predetermined position to thereby bring about a taking-out position, whereby as in the second embodiment, the sheet supplying position and the sheet taking-out position can be changed in the vertical direction. As described above, the sheet supplying position and sheet taking-out position of the lifter plate 103 can also be suitably set in conformity with the worker.

As the means for detecting the upper surface of the sheets, besides the above-described sensor, a reflection type sensor may be provided on the upper portion of the sheet deck and light may be applied to the upper surface of the sheets so that the height of the upper surface of the sheets may be detected by the level of the reflected light thereof.

While in the present embodiment, the paper deck 100 which is the sheet feeding apparatus is connected to the copying machine 400, the paper deck may be contained in the main body of the copying machine 400.

This application claims priority from Japanese Patent Application No. 2003-307156 filed Aug. 29, 2003, which is hereby incorporated by reference herein. 

1. A sheet feeding apparatus comprising: sheet stacking means movable up and down with a plurality of sheets stacked thereon; sheet feeding means for feeding out the sheets stacked on said sheet stacking means; and control means for automatically moving an upper surface of sheet stacked on said sheet stacking means to a sheet supplying position each time the sheet is supplied and to a sheet taking-out position each time the sheet is taken out, wherein said sheet supplying position and said sheet taking-out position are respectively set between an upper limit position and a lower limit position in a range of the upward and downward movement of said sheet stacking means.
 2. A sheet feeding apparatus according to claim 1, further comprising: position detecting means for detecting the position of the upper surface of the sheets stacked on said sheet stacking means; and lift means for moving said sheet stacking means up and down; wherein said control means controls said lift means on the basis of detection by said position detecting means to thereby move said sheet stacking means down so the upper surface of the stacked sheet may be moved to said sheet supplying position when the sheets have been supplied to said sheet stacking means, and move said sheet stacking means up so that the upper surface of the stacked sheets may be moved to said sheet taking-out position when the sheets have been taken out.
 3. A sheet feeding apparatus according to claim 2, wherein said position detecting means is provided with two sensors disposed in the direction of upward and downward movement of said sheet stacking means for detecting the position of the upper surface of the sheets stacked on said sheet stacking means, and said control means moves down said upper surface of the sheets stacked on said sheet stacking means to said sheet supplying position on the basis of detection by the upper one of said two sensors when the sheets have been supplied, and said control means moves up said upper surface of the sheets stacked on said sheet stacking means to sheet taking-out position on the basis of detection by the lower one of said two sensors when the sheets have been taken out.
 4. A sheet feeding apparatus according to claim 2, wherein said position detecting means is a sensor extending in the stack direction of the sheets and capable of detecting the position of the upper surface of the stacked sheets, and said control means moves said sheet stacking means up or down so that said upper surface of the sheets may be moved to said sheet supplying position or said sheet taking-out position when any fluctuation in the position of the upper surface of the sheets has occurred.
 5. A sheet feeding apparatus according to claim 3, wherein said sheet taking-out position and said sheet supplying position are set so that said sheet taking-out position may be higher than said sheet supplying position.
 6. A sheet feeding apparatus having: a lifter plate provided for upward and downward movement; a lifter motor for moving said lifter plate up and down; a pickup roller for feeding out sheets stacked on said lifter plate; and a controller for controlling said lifter motor to thereby move said lifter plate up and down; wherein said controller automatically moves an upper surface of sheet stacked on said lifter plate to a sheet supplying position each time the sheet is supplied and to a sheet taking-out position each time the sheet is taken out, wherein said sheet supplying position and said sheet taking-out position are respectively set between an upper limit position and a lower limit position in a range of the upward and downward movement of said lifter plate.
 7. A sheet feeding apparatus according to claim 6, further comprising: two sheet surface detection sensors disposed in the direction of upward and downward movement of said lifter plate, and wherein said controller controls the lifter motor in the following manner; when the sheet have been supplied said lifter plate is moved down on the basis of detection by the upper one of said two sheet surface detection sensors so that the upper surface of the sheets stacked on said lifter plate is moved said sheet supplying position, and when the sheets have been taken out, said lifter plate is moved up on the basis of detection by the upper one of said two sheet surface detection sensors so that the upper surface of the sheets stacked on said lifter plate may be moved to said sheet taking-out position.
 8. A sheet feeding apparatus according to claim 6 or 7, wherein said sheet taking-out position and said sheet supplying position are set so that said sheet taking-out position is higher than said sheet supplying position.
 9. An image forming apparatus provided with a sheet feeding apparatus according to any one of claims 1 to 5, and an image forming portion for forming an image on a sheet fed from said sheet feeding apparatus. 